The ability to replicate natural materials has substantially improved over the years. For example, decorative laminates have replaced natural materials in the construction of furniture, cabinets, counter tops and other surfaces. In each of these applications, a decorative surface may be applied to a core layer or substrate, namely, plywood, particle board, chipboard, medium density fiberboard, etc. Often, a backing layer is secured to the opposite side of the substrate to balance the laminates or provide other benefits.
Generally, the decorative surface and the backing layer will include one or more kraft paper layers which are adhesively laminated together using various materials, such as melamine formaldehyde and phenolic resins. For example, a high pressure decorative laminate may comprise a very thin overlay sheet impregnated with melamine resin and having aluminum oxide grit to provide for abrasion resistance, a decorative sheet disposed thereunder, and several sheets of kraft paper impregnated with phenolic resin disposed below the decorative sheet.
Typically, in prior art systems, sheets of kraft paper are impregnated with phenolic resin by submerging them in a vat which is filled with phenolic resin and then curing the phenolic resin impregnated kraft paper. The kraft paper soaks up a desired amount of phenolic resin based on the time it is left in the vat and the level of submergence. This method of impregnating the kraft paper is generally not cost effective as it requires large vats providing substantial resin pool surface areas in order to allow the proper immersion of a portion of a continuous roll of kraft paper. These large pool surface areas result in wasteful use of phenolic resin as the large vat surface area is prone to collection of contaminants and to the escaping of resin vapors thus causing variations in the percentage of solids and/or other controlled attributes of the resin requiring substantial portions of the resin to be disposed of from time to time. Moreover, when the resin impregnated kraft paper is being manufactured using such vats, fumes are created during the process which are harmful to the workers in the vicinity of the manufacturing process. All of this is compounded by the fact that such vats of phenolic resin, or other resins, are difficult to clean requiring an inordinate amount of time to properly clean the vats that have been used for impregnating the kraft sheets with phenolic resin.
Conventional laminates are produced by applying heat and pressure to an assembly of laminate material, which typically comprises a plurality of phenol formaldehyde resin impregnated kraft paper sheets, a melamine formaldehyde resin impregnated decorative sheet, and optionally a melamine formaldehyde resin impregnated overlay sheet in a multi-opening press at high temperature and pressure. The different layers or sheets will be mechanically bonded due to the cross link between the resins caused by the heat and pressure.
The laminates which are manufactured by using the kraft paper sheets as described above are made by a bulky manufacturing press which is expensive to operate. Thus, it is not cost effective or desirable to use the press to produce individual laminates. Therefore, in the typical manufacturing process a plurality of laminates are produced from each press during each press cycle to make the most efficient use of the press. As shown in FIG. 1, each laminate assembly 11 may commonly comprise of a melamine overlay layer 12 incorporating AlO2 for wear resistance, a pattern layer 13, and two layers 14 and 15 of phenolic resin impregnated kraft paper.
Typically, in such a press system pairs of such laminate assemblies are positioned back-to-back with the phenolic resin impregnated kraft paper sheet 15 of one laminate assembly facing the phenolic resin impregnated kraft paper sheet of a second laminate assembly. Pairs of laminate assemblies are separated from the other by metal sheets or press plates. However, when the laminate assemblies are pressed together, the different laminate assemblies would stick together if not provided with a release mechanism because the phenolic resins impregnated in the back-to-back kraft paper sheets of the two laminate assemblies would cross link to provide a mechanical bond between the sheets.
Therefore, typically during the manufacturing process each laminate assembly 11 also includes a sheet, known as release sheet. The release sheet is usually kraft paper which has been coated with a release agent on at least one side. This release sheet is placed at the end of each laminate assembly, adjacent to the phenolic resin impregnated kraft paper layer 15, away from the press plates, to provide a release mechanism between the paired laminate assemblies. The release sheet facilitates easy separation of the laminate assemblies after pressing, as the release agent will not allow cross linking of the laminate assemblies, at least with respect to the side of the laminate assembly to which the release sheet is applied.
Typically due to the heat and pressure applied during the pressing process the release sheet sticks to the phenolic resin impregnated kraft paper layer disposed on a side of the release sheet not treated with the release agent as the phenolic resin in this sheet will migrate under heat and pressure into at least a portion of the release sheet to provide structural cross linking. Accordingly, the release sheet generally adds to the thickness or bulk of the laminate. However, due to the presence of the release agent on the other side of the release sheet, the pressed laminate assemblies may then be separated from each other and the side of the kraft paper with the release sheet is sanded to remove the release agent from the surface of the release sheet.
The use of the release sheet during pressing of laminate assemblies as described above and the subsequent sanding of the release agent coated surface presents certain disadvantages. In order to achieve the desired thickness of the laminate assembly and still allow the use of a discrete release sheet to facilitate separation of the laminate assemblies, more sheets of thinner material instead of fewer sheets of thicker material have to be used. This increases the manufacturing overhead as a greater number of sheets have to be handled and processed before they can be used in the laminate assembly. Such handling and processing may include impregnating the sheets with phenolic resin, cutting the sheets to the desired size, and collating the sheets for subsequent pressing. Also, the release sheet itself has to be coated with a release agent, cut to the desired size and collated with the other sheets.
Furthermore, since the release sheet becomes part of the laminate after pressing, at least one sheet of the laminate does not include phenolic resin saturation, but rather relies on migration of the resin from an adjoining sheet. Thus, prior art systems do not provide consistent structural bonding between the different layers of the laminate. Moreover, in order to remove all the release agent from the laminate assembly, it might be necessary to sand more than just the surface of the release sheet. Thus, laminate assemblies obtained by this process may not have a consistent thickness from one laminate assembly to another and also cause wastage of material.
The conventional laminates produced by the above described prior art systems may then be cut to size and employed in a variety of applications such as decorative surfaces for desktops, tabletops, wall panels, and the like such as by bonding them to a core layer or substrate with a conventional adhesive such as contact cement. These laminates may also be used as backer layers common in laminated flooring products.
It should be clear that the use of the release sheet contributes substantially to the cost of the manufactured laminate and also adds to the product cycle time. Not only are there raw material costs involved with the use of a separate release sheet, but also substantial undesirable processing costs are inherent with the use of the release sheets.
Thus, there is a need in the art for a system and method of manufacturing laminates using the advantages offered by bulk pressing the laminates without introducing unnecessary costs, handling steps, or structural disadvantages attendant with the use of prior art release sheets.